Antenna construction



Oct. 2, 1945. ALFORD ETAL 2,385,783

ANTENNA CONSTRUCTION Filed Sept. 50, 1942 INVENTORS ANDREW fill-0RD BY ir iw I ATTORNEY Patented Oct. 2, 1945 ANTENNA CONSTRUCTION Andrew Alford and Morton Fuchs, New York, 7 N. Y., assignors to Federal Telephone and Radio Corporation, a corporation of Delaware Application September 30,1942, SerialNo. 460,290 V 9 Claims.

This invention relates. to antenna systems and more particularly to vertical antenna arrange-v ments.

One of. the objects of this invention is to provide a vertical antenna arrangement having substantially symmetrical radiation and. wherein.

high frequency'cu'rrents heretofore induced in the supporting structure are greatly reduced if notsubstantially eliminated. 1,

Another object of this invention is to provide a vertical antenna having radiators of low surge impedance so that a transmission line to be connected thereto may be matched thereto over a wide frequency band.

Still another object of this invention is to provide a sturdy vertical antenna arrangement which.

is simple in construction, adjustable for different wavelengths.

Vertical antenna arrangements are often. mounted on metallic masts with the upper radiator thereof. extending above the top of the mast and the lower radiator immediatelytherebelow but'some distance above ground. This arrange ment provides dissimilar impedance character-is ties for the two radiators resulting in the occurrence of high frequency currents in this support-- ing mast. In accordance with this invention this difliculty is overcome byextending the mast upon which the radiators are mounted to at least the upper end'of the upper radiator.-- This relationship produces an effect upon the surge impedance of the upper radiator substantially equal to the effect produced on the surge impedance of the lower radiator by-the portion 'ofthe 'mast extending therethrough. -Thesymmetry of radiation pattern of the radiators may be'further improved by extending the mast ashortdistance above the upper radiatorso thatan .end effect is established between the mastandthe upper end of the upperradiatorwhich is similar to that of the effect between thebottom endof the lower radiator and the ;,portion of the. mast extending therebelow to ground. While the mast, may either be solid or hollow, the latter is pre ferred. The transmission line is preferabl ex tended up through the mast to be shielded thereby. to a point between the two radiators to which the conductors. of the transmission, line are connected'. 'Ih radiators maybe of janysuitable shape, but in accordance with a further feature of this invention preferablycompriseho1low"cy lindrical or approximately cylindrical members mounted 'co-axially about the mast;

The radiation pattern of the antenna arrangement or this inventlon'is' enhanced by aiproperselection of the radiator lengths with respect to the wavelength for which theantenna is used. For hollow cylindrical radiators energy radiates inwardly tending to induce a flow of electrical energy along the mast which, with cylindrical radiator, forms effectively a coaxial line, producing an effective shunt to the feed line-at. the feedingpoint. By making the radiators 1 ach a half wavelength lon we discovered that this shunting effect is greatly diminished, if not substantially eliminated. This we believeis because half wavelength radiators provide in effect open ended one half wavelength lines with respect to, the mast thereby presenting at the transmission line connections to the; radiators a very'high or infinite impedance. This improves the impedance characteristics of the antenna as seen from the transmissionline.

In accordancewitha further feature of this invention, the hollow cylindrical radiator members are. preferably so proportioned-as to present,

a fairly low impedance (about 400 ohms or less),

as viewed from the point, of t etransmission,

line connections thereto. To match this low surgerimpedancev with a two-wire transmission line we. construct the transmission line in the form of an aperiodic impedance transformer made in several sections.

-For afurther understanding of the invention, reference may be ,had to the following detailed description to be read in connection with the accompanying, drawing, in which,

' Fig. 1 is a perspective view with partsuin sec-; tion of one form of dipole antenna in accordance with this invention;

Fig. 2 is a fragmentary view in vertical elevationof another form of antenna system of this invention with parts broken away; and

Figs. 3 and''are cross-sectional views taken along lines 3 -.-.3 and .44 respectively of Fig. 2.

Referring to Fig. 1 of thedrawing, antenna comprises twohollow cylindrical radiators l0 and I2 mounted in co-axial relation on a mast M. The mast i4 is hollow and is provided with an opening 16 adjacent the base thereof through which a transmission line l8 from eithera transmitter or receiver 20 is extended. The transmission line extends upwardly in'the hollow mast to and through an outlet opening 22 for connection v sections as indicated by the tapering portions 26.

ass rts By this latter arrangement impedancematching of the antenna structure'over a relatively winerange of frequencies is accomplished,

and the portion of the mast lfiz' i v. 'li'ig'th need only extend a few inches above radiator since very little change in the end effe is produced when this extended portiohb'fthe mast is increased beyond six inches for halfwavelength radiators.

i Theradiators mend 3 I 2 in ay beef almostany Radiators one-half we giveth' most efiici'ent ope explained, that is;- for thisany the coaxial on-as hereinbeforeline-'- is substanti liyemniriatds While we prefer the halfllwaveo-rs may lbe of-"shorter lengthmngtn, the rauiat wni beexperiehcedfi For adua-rter-wavelerigth, fer-example; an open tw ethe radiators-arid; emasts" rnisiowers 1311' became at-thie li'ri "eonnction'and -a'short substantially as shownby the'uot-and dasn hnes' 30' and- 315- radiators: ealt-Wavelength long, the voltage distribution ve are substahtially as indi'catedb Y-the-broken hnes 32' and 34. The iatter I voltage-distribution efiec'ts l are sub eta tially symmetficenanm'prvide in; effect a desired horizontal radiatidfi lobe patterh as in-. dieated bytheline- 35. 13

In Figs. 2 3 and 4, we ve shownanother form'- of antenna-cohstruction ot this invention whereinth r'adi'at' s ean b adjusted? in l'e'ngth for-"operation at d-ifiei' e'nt 'avelehgths, it being understood, of course, the, "fie'etiv'e radiator lengths-equal to one-half: 0 he wavelengths-are preferredfor the sake ofieflicieney and symmetryfl of th e radiation-pattern.- Th'e mast 4ll isi-pref erably cylindrical :and suppiontsan upner radiator 4- I: and -a 1ower:radiator =42 of tlre form illustrated in-Fi'g'; The radiator constructions are li'den f tical and a detailed descriptioII ofithlbtrr-rallia ato'p M W ilLsufii'oeL- i 1 f j In brder.torprouidetfonlengthwise.adjustment of the radiator; "42 ,e' thei radiator; is m'adej up of twoltelescoping substantially.cylindricallsections 43 44.;Tliejnner sec-tiohr43 comprises a. 12's.. side'dzsleeve whilethe fouter section;44.-c'ompri"ses a Gt-sided or hexagonal sleeve-Awe. find that radiator: sleevesvofi.thislshape .are easily:- cohstructe'd' "from lsheeti mat'erialii by a relatively simple stampin'gl opera'tiion', thesleeve beingfnade up of "thre'e piecesrhaving: 'ed'ge flanges; 4.6;andL4'l whichwhen assembled together a are. secured. by any isuitablmethod such vas soldering; brazing, weldin'g etce The inner sleeve. 43=isti1tight13t mounted Ion; the; mast 4.0 .by. means: ofga'nnular insulatorsjq and 154L1'Th insulator 5.0.;a1s ,sup'L- 53: Th'e larger insulator 54sismount'ed about'the mast bys mea-nsiof. a": supporting ring: 55: bolted tothe linnen peripheral; portion :of the. insulator tit-oi a'wav'e alf I f a: wavelength; length. long, however quarter-- 'wavelen g'th line: effect-1 vv iHi-b'e'h'ad be 54. Mounted to the outer peripheral portion of the insulator 54 is a metal ring 56 to which a series of studs 51 are secured through openings contained in the insulator. The inner sleeve 43 is secured as by welding to the ring 56. At the outer edge of thering is mounted a reinforcing sleeve 58 which is adapted to receive along the inner esurfaceflthereof the end of flthe outer h n '16 is' desirable to in'crea'se'theeifective length of the radiator 42, the outer sleeve 44 which is coaxially mounted on the mast 49 by anuihsiila'tor 59 similar to the insulating supped axially with respect to The two sleeves are nort 'by Wing bolts 60 which are 866111641 to the' inner sleeve 43 by nuts 6|, Figs. 2am 3; 'tl 1eo'uter sleeve 44 being provided with sl ts. 63 -thr0ugh which the wing bolts 68) extend. Tdinoii the outer sleeve 44 with respect to the inner sleeve; 4.3; the .wing. bolts. Gfiz'are loosened. The-mounting oft thezouterrsleevezomtheimastiat; the insulator 59 is suificiently loose to permit telescoping movement-of; theesleeve 44h 'Whena desired length. iseobtained 'ithemwing bolts :60,- are tightened .Ltliereby maintaining sleeves. at. the Adesired;bverallzlength;;.; U The; connectionsubetween; the .trananissiqnzline; 10 to the two radiatorsgiis;hroughtiouteofizthei mastA 0;; throughalsealed dublQEOGnXlfiCfiQTIIShQWn memes-section ini'igz This :outletoonnection.

comprises two outletopenings; IH and. 12s Teaphi of which is .providedWith aperipherahfiamge;13;; Mounted on the flange is a gasketzflflaand: anon? sulator, 16 whichzis securedtogthegflange 131m studsvllh The,,centenlportionwjofgthe .insnlatbr; 1,6. is provided- Twitli'. 5a; terrninalgnconnectionrfl 0.;- which extends therethrough the connectionhaw ing an axial xopening;through;which to; receive one. of; the' wircs 8130f: the; transmission 411111210.

' Thewire 82 may; he wpreferably;clamped to. $118" connector; by.a.cnut;83 andthemconnented't one A of; thei studs; 51.: :threadablx :received Lin metaIringN-EBe-U v 1 Fmmthe toregoiJn eitz illheclearrthatgtneana tenna.construction;risgcsturdrzeeasily 'icmanufacel tursednandnmvides for-zadiustmentz ffer different wavelengths; :It 1-. thatitheiradiatonc t otion lent; that isithe EIQP ItiQ -E thereo fishealed} tame-properwave eneth madin .1 oiltheradia or t.

While we :have shot and; described enlyetwo embodimentsiof the invention, weleoog-nizeethait; manyrantenna; systems .of other id'esigxfsi ahdgare 1 rangements may be. madeihcorporating thesyim-s metrical radiationandlimpedanceiinatchihg fe turesthereof without nepmmgemm the' inyenlf tion'. It will be un'ders r effect produced by the lower portion of the mast on the lower radiator.

2. The vertical antenna defined in claim 1 wherein the radiators comprise hollow substantially cylindrical members mounted co-axially with respect to the mast.

3. The vertical antenna defined in claim 1 wherein each of the radiators comprise a pair of telescoping sleeves whereby the axial length of each radiator can be adjusted.

4. The vertical antenna defined in claim 1 wherein each of the radiators is electrically substantially a half wavelength long.

5. A vertical antenna comprising a conductive mast, a shielded transmission line extending to a given point up on said mast, two radiators each surrounding said mast and connected to said transmission line, one of the radiators being disposed a relatively short distance above said point and the other disposed a relatively short distance below said point, and said mast having a portion extending above the upper radiator to produce an upper end capacity effect substantially similar to an end capacity efiect produced at the bottom of the lower radiator by the portion of the mast extending therebelow.

6. The vertical antenna defined in claim 5 wherein the two radiators comprise hollow sleeves of a size having a relatively low surge impedance and said transmission line being constructed to substantially match the surge impedance of said radiators.

7. A vertical antenna comprising a hollow conductive mast, a transmission line extending upwardly in said mast so as to be shielded thereby, two hollow substantially cylindrical radiator members disposed in end to end relation to each other and co-axially with respect to said mast, said transmission line being connected to said radiators, and said radiators being so disposed with respect to the length of said mast that a portion of the mast extends above the upper radiator sufiicient to produce a capacity eflect therewith substantially equal to the capacity effect produced with the lower radiator by the portion of the mast extending below the lower radiator.

8. A vertical antenna comprising a hollow conductive mast, a transmission line extending upwardly in said mast so as to be shielded thereby, two hollow substantially cylindrical radiator members disposed in end to end relation to each other and co-axially with respect to said mast and spaced apart a relatively short distance, said transmission line being connected to said radiators, said two radiators being of a size having a relatively low impedance and said transmission line being constructed of a plurality of aperiodic impedance transformer sections to substantially match the surge impedance of said radiators over a wide frequency band.

9. The antenna defined in claim 8 wherein each of the radiators are adjustablein length and a change in the surge impedance thereof due to a change in length can be matched at the transmission line connection by shifting the connection with respect to one of the transformer sections of the line.

ANDREW ALFORD. MORTON FUCHS. 

